Podcast
Questions and Answers
What is the primary cause of Turner’s syndrome?
What is the primary cause of Turner’s syndrome?
Which of the following characteristics is associated with Klinefelter syndrome?
Which of the following characteristics is associated with Klinefelter syndrome?
What defines a mosaic individual in terms of chromosomal anomalies?
What defines a mosaic individual in terms of chromosomal anomalies?
Which of the following best describes a Robertsonian translocation?
Which of the following best describes a Robertsonian translocation?
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Which type of cellular event typically leads to numerical mosaic anomalies?
Which type of cellular event typically leads to numerical mosaic anomalies?
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How are mosaic individuals denoted in genetic notation?
How are mosaic individuals denoted in genetic notation?
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What is a key difference between mosaicism and chimerism?
What is a key difference between mosaicism and chimerism?
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Which type of structural chromosomal anomaly is associated with chronic myelogenous leukemia (CML)?
Which type of structural chromosomal anomaly is associated with chronic myelogenous leukemia (CML)?
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What is the phenotypic outcome of individuals with Robertsonian translocation?
What is the phenotypic outcome of individuals with Robertsonian translocation?
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What occurs during prophase of mitosis?
What occurs during prophase of mitosis?
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What type of chromosomal anomaly entails the loss of a segment from a chromosome?
What type of chromosomal anomaly entails the loss of a segment from a chromosome?
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What is the consequence of non-disjunction during meiosis?
What is the consequence of non-disjunction during meiosis?
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Which chromosomal abnormality is characterized by having an extra chromosome?
Which chromosomal abnormality is characterized by having an extra chromosome?
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During which phase do chromosomes align at the equatorial plane in mitosis?
During which phase do chromosomes align at the equatorial plane in mitosis?
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What defines Turner’s syndrome in terms of chromosomal composition?
What defines Turner’s syndrome in terms of chromosomal composition?
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What is the outcome of non-disjunction during the first meiotic division?
What is the outcome of non-disjunction during the first meiotic division?
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What type of offspring results from fertilization involving a normal gamete and a gamete with an extra autosome?
What type of offspring results from fertilization involving a normal gamete and a gamete with an extra autosome?
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What happens during anaphase of mitosis?
What happens during anaphase of mitosis?
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Which of these statements is true regarding meiosis?
Which of these statements is true regarding meiosis?
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Which of the following is a characteristic feature of Down syndrome?
Which of the following is a characteristic feature of Down syndrome?
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Which chromosomal abnormality is categorized as a structural anomaly?
Which chromosomal abnormality is categorized as a structural anomaly?
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Which phase follows telophase during the mitotic cell cycle?
Which phase follows telophase during the mitotic cell cycle?
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What typically increases the incidence of trisomy 21?
What typically increases the incidence of trisomy 21?
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What is the primary purpose of the mitotic spindle during mitosis?
What is the primary purpose of the mitotic spindle during mitosis?
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Which of the following is NOT a common anomaly associated with Edward's syndrome (Trisomy 18)?
Which of the following is NOT a common anomaly associated with Edward's syndrome (Trisomy 18)?
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How is Patau syndrome (Trisomy 13) primarily linked to chromosomal abnormalities?
How is Patau syndrome (Trisomy 13) primarily linked to chromosomal abnormalities?
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What is a unique aspect of a nullosomic gamete?
What is a unique aspect of a nullosomic gamete?
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Which karyotype corresponds to Down syndrome?
Which karyotype corresponds to Down syndrome?
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Which of the following statements is true regarding numerical chromosomal anomalies?
Which of the following statements is true regarding numerical chromosomal anomalies?
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What is the typical outcome for infants born with Patau syndrome?
What is the typical outcome for infants born with Patau syndrome?
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What type of chromosomal deletion involves the loss of a segment of chromosome without any attached genetic material at the ends?
What type of chromosomal deletion involves the loss of a segment of chromosome without any attached genetic material at the ends?
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Which karyotype notation indicates a deletion occurring between specific breakpoints within a chromosome?
Which karyotype notation indicates a deletion occurring between specific breakpoints within a chromosome?
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What type of chromosomal rearrangement is characterized by a segment of a chromosome breaking off and reinserting itself at the same chromosome but in reverse order?
What type of chromosomal rearrangement is characterized by a segment of a chromosome breaking off and reinserting itself at the same chromosome but in reverse order?
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How are isochromosomes formed?
How are isochromosomes formed?
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Which statement accurately describes ring chromosomes?
Which statement accurately describes ring chromosomes?
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What is the outcome of nondisjunction during meiotic division?
What is the outcome of nondisjunction during meiotic division?
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What distinguishes mosaicism from chimerism in genetic abnormalities?
What distinguishes mosaicism from chimerism in genetic abnormalities?
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Which type of chromosomal abnormality includes both balanced and unbalanced forms?
Which type of chromosomal abnormality includes both balanced and unbalanced forms?
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What is a characteristic feature of pericentric inversions?
What is a characteristic feature of pericentric inversions?
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What is indicated by the karyotype notation 46,XY,del(7)(q11.23q21.2)?
What is indicated by the karyotype notation 46,XY,del(7)(q11.23q21.2)?
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Study Notes
Mitosis & Meiosis
- Mitosis consists of a cell cycle with G1, S, and G2 phases; interphase precedes division.
- G1 phase contains one diploid cell; in the S phase, DNA is duplicated forming two sister chromatids.
- G2 phase prepares chromosomes for condensation; two daughter cells produced carry equal genetic information.
- Mitosis phases include:
- Prophase: Mitotic spindle forms, centrosomes pair.
- Prometaphase: Nuclear membrane dissolves, chromosomes attach to spindle microtubules.
- Metaphase: Chromosomes align at the equator.
- Anaphase: Sister chromatids separate at centromeres.
- Telophase: Chromosomes de-condense, nuclear membranes reform.
Non-disjunction and its Impact on Meiosis
- Non-disjunction refers to the failure of chromosomes to separate properly during meiosis.
- This leads to aneuploidy, the presence of an abnormal number of chromosomes in a cell.
- Non-disjunction can occur in:
- Meiosis I: Leads to four unbalanced gametes.
- Meiosis II: Results in two normal and two unbalanced gametes.
- Resultant gametes can produce monosomic (missing one chromosome) or trisomic (extra chromosome) offspring.
Classifications of Chromosomal Abnormalities
- Chromosomal anomalies can be classified into numerical and structural abnormalities.
- Numerical abnormalities alter complete haploid sets (n) of chromosomes.
- Structural abnormalities affect chromosome structure and organization.
Numerical Chromosomal Anomalies
-
Down Syndrome (Trisomy 21):
- Karyotype: 47, XY, +21.
- Most cases result from maternal non-disjunction; incidence rises with maternal age.
- Symptoms: Facial dysmorphology, intellectual disability (IQ < 50).
-
Edward's Syndrome (Trisomy 18):
- Karyotype: 47, XY, +18.
- Occurs in approximately 1 in 6,000 live births; high mortality in infancy.
- Common anomalies: Heart defects, kidney malformations.
-
Patau Syndrome (Trisomy 13):
- Karyotype: 47, XY, +13.
- Half of affected individuals die within the first month; limited survival beyond one year.
- Presents multiple dysmorphic features.
Numerical Sex Chromosome Anomalies
-
Turner's Syndrome (Monosomy X):
- Karyotype: 45,XO; occurs in 1 in 4,000 females.
- The only viable monosomy; traits include short stature and webbed neck.
-
Klinefelter Syndrome:
- Karyotype: 47, XXY; affects about 1 in 600 males.
- Results from nondisjunction during maternal meiosis I; symptoms include breast enlargement and sterility.
Mosaicism
- Defined as the presence of genetically distinct cell lines derived from a single zygote.
- Denoted in karyotypes (e.g., 46, XY / 47, XY, +21).
- Caused by mitotic non-disjunction; not to be confused with chimerism (from multiple zygotes).
Structural Chromosomal Anomalies
-
Reciprocal Translocation:
- Involves exchange between two non-homologous chromosomes (e.g., Philadelphia chromosome linked to CML).
-
Robertsonian Translocation:
- Loss of short arms from acrocentric chromosomes, resulting in fusion of long arms; carriers have 45 chromosomes.
-
Deletion:
- Refers to the loss of chromosome segments; indicated as "del" in nomenclature.
-
Inversion:
- Involves segments breaking and rejoining; categorized as pericentric or paracentric.
-
Isochromosome:
- Occurs when centromeres divide transversely, resulting in chromosome duplication along one arm.
-
Ring Chromosome:
- Formed when breaks on each arm reunite as a ring structure; often unstable in mitosis.
Take Home Message
- Chromosome abnormalities can be classified into numerical and structural, impacting genetic stability.
- Normal meiosis results in four haploid gametes; non-disjunction leads to trisomy or monosomy.
- Mosaicism arises from a single zygote; chimerism from fusion of multiple zygotes.
- Structural abnormalities include various rearrangements, each affecting genetic expression differently.
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Description
This quiz covers key concepts related to chromosome anomalies, focusing on mitosis and meiosis events. It examines non-disjunction and its consequences, as well as various chromosomal abnormalities, including numerical and structural categories. Students will also explore common disorders like trisomies and Turner’s syndrome.
